make ConstEvaluatable more strict

Author: lcnr

compiler/rustc_middle/src/mir/mod.rs

@@ -186,6 +186,19 @@ pub struct Body<'tcx> {
     /// FIXME(oli-obk): rewrite the promoted during promotion to eliminate the cell components.
     pub ignore_interior_mut_in_const_validation: bool,
 
+    /// Does this body use generic parameters. This is used for the `ConstEvaluatable` check.
+    ///
+    /// Note that this does not actually mean that this body is not computable right now.
+    /// The repeat count in the following example is polymorphic, but can still be evaluated
+    /// without knowing anything about the type parameter `T`.
+    ///
+    /// ```rust
+    /// fn test<T>() {
+    ///     let _ = [0; std::mem::size_of::<*mut T>()];
+    /// }
+    /// ```
+    pub is_polymorphic: bool,
+
     predecessor_cache: PredecessorCache,
 }
 
@@ -208,7 +221,7 @@ impl<'tcx> Body<'tcx> {
             local_decls.len()
         );
 
-        Body {
+        let mut body = Body {
             phase: MirPhase::Build,
             basic_blocks,
             source_scopes,
@@ -224,8 +237,11 @@ impl<'tcx> Body<'tcx> {
             span,
             required_consts: Vec::new(),
             ignore_interior_mut_in_const_validation: false,
+            is_polymorphic: false,
             predecessor_cache: PredecessorCache::new(),
-        }
+        };
+        body.is_polymorphic = body.has_param_types_or_consts();
+        body
     }
 
     /// Returns a partially initialized MIR body containing only a list of basic blocks.
@@ -234,7 +250,7 @@ impl<'tcx> Body<'tcx> {
     /// is only useful for testing but cannot be `#[cfg(test)]` because it is used in a different
     /// crate.
     pub fn new_cfg_only(basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>) -> Self {
-        Body {
+        let mut body = Body {
             phase: MirPhase::Build,
             basic_blocks,
             source_scopes: IndexVec::new(),
@@ -250,8 +266,11 @@ impl<'tcx> Body<'tcx> {
             generator_kind: None,
             var_debug_info: Vec::new(),
             ignore_interior_mut_in_const_validation: false,
+            is_polymorphic: false,
             predecessor_cache: PredecessorCache::new(),
-        }
+        };
+        body.is_polymorphic = body.has_param_types_or_consts();
+        body
     }
 
     #[inline]

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -10,6 +10,7 @@ use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::{self, Binder, Const, Ty, TypeFoldable};
 use std::marker::PhantomData;
 
+use super::const_evaluatable;
 use super::project;
 use super::select::SelectionContext;
 use super::wf;
@@ -458,16 +459,17 @@ impl<'a, 'b, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'tcx> {
                 }
 
                 ty::PredicateAtom::ConstEvaluatable(def_id, substs) => {
-                    match self.selcx.infcx().const_eval_resolve(
-                        obligation.param_env,
+                    const_evaluatable::is_const_evaluatable(
+                        self.selcx.infcx(),
                         def_id,
                         substs,
-                        None,
-                        Some(obligation.cause.span),
-                    ) {
-                        Ok(_) => ProcessResult::Changed(vec![]),
-                        Err(err) => ProcessResult::Error(CodeSelectionError(ConstEvalFailure(err))),
-                    }
+                        obligation.param_env,
+                        obligation.cause.span,
+                    )
+                    .map_or_else(
+                        |e| ProcessResult::Error(CodeSelectionError(ConstEvalFailure(e))),
+                        |()| ProcessResult::Changed(vec![]),
+                    )
                 }
 
                 ty::PredicateAtom::ConstEquate(c1, c2) => {

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -7,6 +7,7 @@ pub mod auto_trait;
 mod chalk_fulfill;
 pub mod codegen;
 mod coherence;
+mod const_evaluatable;
 mod engine;
 pub mod error_reporting;
 mod fulfill;

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -6,6 +6,7 @@ use self::EvaluationResult::*;
 use self::SelectionCandidate::*;
 
 use super::coherence::{self, Conflict};
+use super::const_evaluatable;
 use super::project;
 use super::project::normalize_with_depth_to;
 use super::util;
@@ -542,17 +543,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
 
             ty::PredicateAtom::ConstEvaluatable(def_id, substs) => {
-                match self.tcx().const_eval_resolve(
-                    obligation.param_env,
+                const_evaluatable::is_const_evaluatable(
+                    self.infcx,
                     def_id,
                     substs,
-                    None,
-                    None,
-                ) {
-                    Ok(_) => Ok(EvaluatedToOk),
-                    Err(ErrorHandled::TooGeneric) => Ok(EvaluatedToAmbig),
-                    Err(_) => Ok(EvaluatedToErr),
-                }
+                    obligation.param_env,
+                    obligation.cause.span,
+                )
+                .map(|()| EvaluatedToOk)
+                .or_else(|e| match e {
+                    ErrorHandled::TooGeneric => Ok(EvaluatedToAmbig),
+                    _ => Ok(EvaluatedToErr),
+                })
             }
 
             ty::PredicateAtom::ConstEquate(c1, c2) => {

src/librustc_trait_selection/traits/const_evaluatable.rs

@@ -0,0 +1,54 @@
+use rustc_middle::ty::{self, TypeFoldable};
+use rustc_infer::infer::InferCtxt;
+use rustc_middle::ty::subst::SubstsRef;
+use rustc_span::Span;
+use rustc_span::def_id::DefId;
+use rustc_middle::mir::interpret::ErrorHandled;
+use rustc_hir::def::DefKind;
+
+pub fn is_const_evaluatable<'cx, 'tcx>(
+    infcx: &InferCtxt<'cx, 'tcx>,
+    def: ty::WithOptConstParam<DefId>,
+    substs: SubstsRef<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    span: Span,
+) -> Result<(), ErrorHandled>
+{
+    let def_kind = infcx.tcx.def_kind(def.did);
+    match def_kind {
+        DefKind::AnonConst => {
+            let mir_body = if let Some(def) = def.as_const_arg() {
+                infcx.tcx.optimized_mir_of_const_arg(def)
+            } else {
+                infcx.tcx.optimized_mir(def.did)
+            };
+            if mir_body.is_polymorphic {
+                return Err(ErrorHandled::TooGeneric);
+            }
+        }
+        _ => {
+            if substs.has_param_types_or_consts() {
+                return Err(ErrorHandled::TooGeneric);
+            }
+        }
+    }
+
+    match infcx.const_eval_resolve(
+        param_env,
+        def,
+        substs,
+        None,
+        Some(span),
+    ) {
+        Ok(_) => Ok(()),
+        Err(err) => {
+            if matches!(err, ErrorHandled::TooGeneric) {
+                infcx.tcx.sess.delay_span_bug(
+                    span,
+                    &format!("ConstEvaluatable too generic: {:?}, {:?}, {:?}", def, substs, param_env),
+                );
+            }
+            Err(err)
+        }
+    }
+}

src/test/ui/const_evaluatable/associated_const.rs

@@ -0,0 +1,11 @@
+// check-pass
+struct Foo<T>(T);
+impl<T> Foo<T> {
+    const VALUE: usize = std::mem::size_of::<T>();
+}
+
+fn test<T>() {
+    let _ = [0; Foo::<u8>::VALUE];
+}
+
+fn main() {}

src/test/ui/enum-discriminant/issue-70453-polymorphic-ctfe.rs

@@ -1,5 +1,3 @@
-// run-pass
-
 #![feature(arbitrary_enum_discriminant, core_intrinsics)]
 
 extern crate core;
@@ -9,6 +7,7 @@ use core::intrinsics::discriminant_value;
 enum MyWeirdOption<T> {
     None = 0,
     Some(T) = core::mem::size_of::<*mut T>(),
+    //~^ ERROR constant expression depends on a generic parameter
 }
 
 fn main() {

src/test/ui/enum-discriminant/issue-70453-polymorphic-ctfe.stderr

@@ -0,0 +1,10 @@
+error: constant expression depends on a generic parameter
+  --> $DIR/issue-70453-polymorphic-ctfe.rs:9:15
+   |
+LL |     Some(T) = core::mem::size_of::<*mut T>(),
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
+error: aborting due to previous error
+

src/test/ui/impl-trait/issue-56445.rs

@@ -5,8 +5,7 @@
 
 use std::marker::PhantomData;
 
-pub struct S<'a>
-{
+pub struct S<'a> {
     pub m1: PhantomData<&'a u8>,
     pub m2: [u8; S::size()],
 }

src/test/ui/lazy_normalization_consts/issue-73980.rs

@@ -1,4 +1,3 @@
-// check-pass
 #![feature(lazy_normalization_consts)]
 #![allow(incomplete_features)]
 
@@ -10,5 +9,6 @@ impl<T: ?Sized> L<T> {
 }
 
 impl<T> X<T, [u8; L::<T>::S]> {}
+//~^ ERROR constant expression depends on a generic parameter
 
 fn main() {}

src/test/ui/lazy_normalization_consts/issue-73980.stderr

@@ -0,0 +1,10 @@
+error: constant expression depends on a generic parameter
+  --> $DIR/issue-73980.rs:11:9
+   |
+LL | impl<T> X<T, [u8; L::<T>::S]> {}
+   |         ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
+error: aborting due to previous error
+